The individual amplification of the sound of musical instruments is now common practice. It appears to be most convenient to control the volume of the amplifying system with a pedal device. This arrangement gives the musician continuing control over the dynamics of his instrument, and frees his hands for their usual functions. One of the usual volume control arrangements for any kind of an electrical circuit is the potentiometer, which is a variable resistance. These units are commonly incorporated in a pedal control, together with a mechanism for converting the angular movement of the pedal into a rotary motion of a potentiometer shaft. The conversion mechanism can be selected from the standard available systems, such as an arcuate rack secured to the pedal and engaging a pinion on the potentiometer shaft, or the ancient bow drill principle, in which a cord is wrapped around a shaft and secured at its ends to two points that move together. When these two points are terminals secured to the moving pedal, it is obvious that pedal movement will induce rotation of the potentiometer shaft. The present invention presents an improvement in this type of device. A problem commonly associated with these controllers occurs particularly when the controller is connected in shunt relationship with the signal pickup on the musical instrument. The controller is thus obviously in shunt relationship also with the amplifier. The volume control is effected by varying the resistance of this shunt, resulting in a maximum volume when the potentiometer is at a maximum resistance. The problem occurs at the other extreme, in which minimum volume in associated with a minimum resistance. The usual potentiometer, even though it may be of a type having a logarithmic resistance gradient, tends to be over-sensitive and erratic at conditions approaching minimum resistance. This is a serious problem to the musician, as this is precisely where he needs the most delicate dynamic control over his instrument.